Evidence suggests that prenatal care, healthy behaviors such as exercise and nutrition, and general stress level are associated with fetal and maternal health but there is a relative dearth of research on interventions to improve these factors in pregnant substance users. Two hundred pregnant substance users entering outpatient substance abuse treatment were randomized to receive either three individual sessions of Motivational Enhancement Therapy for pregnant substance users (MET-PS) or the first three individual sessions normally provided by the program. The present study evaluated the relative efficacy of MET-PS, compared to treatment as usual, on modifiable healthy behaviors and the impact of treatment when the groups were pooled. The results suggest that MET-PS was not more effective than treatment as usual in improving modifiable healthy behaviors. When the treatment groups were pooled, the results suggest that there were significant increases in prenatal care utilization and prenatal/multi-vitamin and water consumption, and a significant decrease in stress. Limitations and recommendations for further research are discussed.